Difference in strain susceptibilities to colon carcinogenesis were studied using azoxymethane (AOM) and 1,2-dimethylhydrazine (DMH) in mice. DMH at levels of 0.2 mole per kilogram mouse did not produce colon tumors in C57BL/6N strain mice, but AOM at 0.1 millimole did produce colon adenocarcinoma. Studies with DBA/2N strain showed similar results. BALB/canN and C3Hf/HeN strains were susceptible to DMH carcinogenesis. 2,4-dimethylmorpholine-nitrosamine (MPN), a dehydrated derivative of 2,2'-dihydroxypropane-nitrosamine (MPN), a potent pancreatic ductular carcinogen, was tested in Syrian golden hamsters. Mainly, liver tumors were found. Thus, MPN is probably not a DIPN metabolite in the production of pancreatic cancer.